1. Field
The present invention relates to orbit determination and maneuver detection. More particularly, the present invention relates to determining orbit state under environments which include full environmental perturbations and satellite maneuvering that requires high fidelity maneuver modeling.
2. Description of the Related Art
Orbit determination refers to the estimation of orbits of spacecraft relative to primary celestial bodies, given applicable measurements. Orbit determination methods produce orbit estimates including errors. Orbit determination methods are generally grouped into three categories including Initial Orbit Determination, Batch Least Squares differential corrections, and Sequential Processing.
Of these orbit determination methods, Initial Orbit Determination (IOD) is a common practice in satellite navigation. An IOD method is generally designed to give an approximation of the orbit of an object, which is then refined with other techniques such as Least Squares, Batch Least Squares and Kalman Filtering. Some of the conventional IOD methods developed include Gauss' Method, which uses angle data only; the Herrick-Gibbs method, which uses three position vectors and times; and Lambert's method, which uses two position vectors and time.
Conventional IOD methods assume a simple two-body model for orbit propagation. In a two-body model, only the effects of the central body (typically the Earth) and the object itself are considered, and the central body is assumed to be spherically symmetric so each body can be modeled as a point mass. These assumptions greatly simplify the model of the orbital motion. However, to accurately model an orbit over a period or hours or days, it is necessary to recognize that the central body is not spherically symmetrical. In addition one must consider other forces such as atmospheric drag and solar radiation pressure. Mechanisms for taking into account maneuvers are often necessary. Improper modeling or ignoring these maneuvers altogether makes for poor or unacceptable orbit solutions. Some methods do exist for solving for these with impulsive changes but this is often insufficient to realistically model the maneuver to a sufficient fidelity.
Further, the process of orbit determination as applied to the case of an on-orbit breakup, for instance due to an explosion or collision, raises difficulties related to determining which observations are associated with which piece of debris. Accordingly, a method and apparatus for initial orbit determination that can be used to help sort the observations into groups that are likely to represent observations of the same piece is needed. Once the observations are sorted, standard orbit determination techniques can be used to refine the estimate of the orbit.